A fan case used for an aircraft engine will briefly be explained.
The fan case is to cover a plurality of fan blades in the aircraft engine and is generally made of metallic material such as titanium alloy. The fan case is able to be fastened to a counterpart with fasteners including fastening bolts and nuts in a state contacting with the counterpart.
As shown in FIG. 4, the fan case has a cylindrical case body 120 as a part body. The case body 120 extends in the direction of a case axis. At least at one end of the case body 120, there is integrally formed a flange 110 through a bend 115 so that the flange is able to be brought into contact with the counterpart. The flange 110 has an insertion hole 112 into which a fastener (fastening bolt) is insertable. On an outer surface of the flange 110 opposite to the counterpart contacting side, there is formed by machining a flat fastening seat 111 that is orthogonal to an outer circumferential surface of the case body 120. The fastening seat 111 is able to support part of the fastener, i.e., the head of a fastening bolt or the bottom surface of a nut. To sufficiently secure fastening strength between the fan case and the counterpart, the center of the insertion hole 112 of the flange 110, i.e., the center of the fastening seat 111 is so set not to be largely separated away from the outer circumferential surface of the case body 120 as illustrated in FIG. 4. Due to this, an area end (area terminal) 114 of a processed area 113 is positioned on a small-diameter curved surface of the bend 115. A related art concerning the present invention is, for example, U.S. Patent Publication No. 2008-011868.